This invention is applicable to the manufacture of steel from solid iron-bearing charge materials in an oxygen steel-making converter. The iron-bearing charge material may include scrap (metal scrap, rolling crop shear, metal waste from the steelmaking industry, etc.) metallized pellets, sponge iron.
There is known a process of making steel in a converter with the use of a metal charge.
According to this process, the converter is to be equipped with bottom and side tuyeres in the form of a pipe-inside-pipe construction in which the central duct is used for the supply of oxygen and the external one for the delivery of a liquid or gaseous hydrocarbon. The process is carried out as follows.
First, the converter is charged with scrap, sponge iron, solid pig iron and the solid iron-bearing materials. The solid charge is preheated to a temperature of 1000.degree.-1200.degree. C. due to complete burning of a liquid or gaseous hydrocarbonaceous material in an oxidizing gas in accordance with the following reactions: ##STR1##
The following reactions proceed in the oxidizing atmosphere: ##STR2##
The products of combustion are mainly CO.sub.2 and H.sub.2 O, as well as iron oxide.
Once molten metal is formed in the region of tuyeres, powdered hydrocarbonaceous materials (such as coke and coal) are fed into the converter to permit carbonization of the melt formed in the course of heating. As this happens, the consumption of the hydrocarbonaceous material is gradually reduced to a level at which the tuyeres are protected from damage, that is, down to 10-12% of the oxygen consumption. The entire metal charge is melted down toward the end of this period.
Next, the melt is refined in accordance with common practice such as performed during blowing of molten pig iron. The heating of the bath is effected by means of the heat resultant from the last-mentioned reaction, with CO prevailing in the flue gases. At the same time, powdered lime is introduced into the bath together with oxygen to form a slag bath.
On reaching a required temperature, the heat is poured into a ladle in which the metal undergoes deoxidation and alloying, and, if necessary, is subjected to further treatment.
The method described above is disadvantageous in that it requires blowing of powdered hydrocarbonaceous materials into the converter, the preparation and transportation of which necessitate installation of auxiliary equipment (mills, pipes for feeding coal-dust fuel) and, consequently, extra capital costs. Another deficiency of the above method is a substantial waste of iron due to its oxidation at the stage of preheating the scrap charged into the converter. The iron oxides make up the base of the first slag, which subsequently interact with the hydrocarbon of the powdered coke or coal injected into the bath, according to the reaction of direct reduction: EQU (FeO)+C=[Fe]+{CO}-38,400 ccal/kg.mol (8)
which requires enormous consumption of heat. This reaction proceeds to increase the time period required for feeding powdered hydrocarbonaceous materials due to lack of heat needed to ensure complete melting-down of the metal scrap. At the same time iron oxide continue to get into the slag since oxidation of iron takes place mainly during oxygen blowing.
The above disadvantages are partly obviated by using lump hydrocarbonaceous fuel (coke or coal). The solid fuel charged with metal scrap ensures, along with the heat released according to the reactions (1)- (4), the heating of the charge due to the heat resultant from the following reaction: EQU C+{O.sub.2 }=CO.sub.2 =94,200 ccal/kg.mol (9)
In addition, the presence of solid hydrocarbonaceous fuel in contact with the metal scrap promotes its quicker melting due to decreasing melting temperature of the charge because of its carbonization. Nevertheless, it has been observed that the time period of the stage at which the charge is completely melted in the course of direct reducing reaction (8) is likewise prolonged even though the heats are operated on a solid fuel. This is established by the fact that on consuming from 40-50 to 70-80 m.sup.3 of oxygen per ton of charge and bringing the temperature up to 1520.degree.-1570.degree. C., the temperature then rises slower than in the previous period. Simultaneously, the slag oxidation rate increases with the amount of iron oxides getting thereinto. This, in turn, results in higher losses of iron due to oxidation, and in a higher flow rate of oxygen. Therefore, to improve thermal balance of the heat, additional heat carriers, such as silicon, aluminum and others should be used to prevent the reaction of direct reduction (8) and, consequently, undesirable losses of heat.
There is known still another steel making process which is operated on solid iron-bearing materials and which makes use of an oxygen converter with combined blowing, wherein oxygen and a powdered hydrocarbonaceous material are concurrently introduced into the bath below the metal level. The amount of steel thus produced exceeds by 10 to 30% the nominal weight of the heat accommodated in a steel-teeming ladle. On tapping the heat and filling the ladle, this additional amount of metal (10-30% of the heat weight) is left in the converter so as to undergo carbonization and then to be alloyed with silicon, for distance, during subsequent tapping of "the additional" metal into an auxiliary ladle, with the amount of silicon to be introduced being calculated in view of obtaining metal with the silicon content of up to 1.5%. The silicon-containing metal is poured from the auxiliary ladle into the converter onto the preheated solid charge to start a new heat. In this way it becomes possible to improve thermal balance of the heat thereby partly eliminating the disadvantages inherent in the above-described process.
However, the last-mentioned steelmaking process is likewise disadvantages in that it requires the use of an auxiliary ladle, which brings down productivity of labour in the shop and increases the consumption of refractories. Furthermore, the operation schedule in the shop is complicated with the introduction of a new process stage, transportation of the auxiliary ladle to the charging bay of the shop where the residual metal is poured into the converter, to say nothing of other additional operations required therefor.